Solid State Phenomena Vols. 124-126

Abstract: As Recently, wafer level packaging (WLP) received lots of attention in system because it shows the potential to reduce packaging cost, while the yield of devices after dicing and packaging can be increased. In this study, we newly proposed WLP for light emitted diodes (LED) using MEMS technology. Our silicon package structure is composed of base and reflector cup. The role of base is that settle LED chip at desired position and supply electrical interconnection for LED operation. Reflector cup was formed by an-isotropic wet etching. Package platform could be fabricated by eutectic bonding between base and reflector cup using AuSn. We carried out process using six sigma methodology. We first decided 2 factors and 3 levels by design of experiment (DOE). One factor is the kind of metal model. The other is the shape of pattern. It was used that three-kind metal models are Au (cup), AuSn (cup), and AuSn (base). The bonding strength is measured using a die shear strength tester. It carried out in the repetition experiment by a unit of 3 times. As a result of this test, the AuSn(base) metal model and the No.3 pattern were applied by the optimal condition. We set the value of the low limit at shear strength 950g/mm2 for applying sigma level. This value is a generally used for eutectic bonding packages. The experiment results have 3.13 sigma level (95% yield). In this paper, We show the final LED package which is finished up to LED attach, wire bonding, encapsulation, etc. This wafer level bonding process demonstrates its promising potential at the wafer level packaging in LED packaging.

Abstract: Self-Assembled Monolayer (SAM) is a single layer of ordered molecules absorbed on a surface by chemical bonding between the molecular head group and the surface. The surface properties can be controlled by the terminal functional group of the SAM layer. In order to utilize SAM layers for device applications, SAM layer needs to be patterned as a sub-micron size. Patterning of SAM layer in sub-micron size has been done by various techniques including direct-writing by dip-pen nano lithography, selective etching with UV photons, and selective deposition of SAM layer by &-contact printing. In this study, silane based SAM layer was patterned to the sub-micron size using zero residual Nano imprint Lithography, which is regarded as next generation lithography technique due to its simplicity, high throughput and high resolution pattern transferring capability. Using zero-residual layer imprinting, 300nm~2um sized SAM patterns can successfully fabricated. In order to check the surface property of patterned SAM layer, a solution containing nano Ag particles was spin-coated on the SAM patterned substrate and nano Ag particles were selectively deposited on the substrate.

Abstract: This paper reviews novel techniques developed in our laboratory to deposit ceramic thin films from aqueous solutions. All the techniques are based on the heterogeneous nucleation and growth phenomenon; ceramic precipitates are prone to be formed preferentially on substrate/solution interfaces when the rate of the formation of the precipitates is appropriately controlled. In “oxidative soak coating” method, metal ions with a lower valence state are oxidized in homogeneous solutions to those with a higher valence state; thereby coatings of SnO2, MnO2, CeO2, Co3O4 and Fe3O4 have been deposited. In “ligand decomposition” method, ligands of an indium peroxo- complex are decomposed to promote spontaneous hydrolysis of the indium ion; thereby In2O3 coating has been deposited. In “enzyme-assisted precipitation” method, precipitant of metal ions is supplied by urease immobilized on a substrate to promote local deposition of ceramics on the substrate, by which hydroxyapatite coating has been rapidly deposited. The control of the rate of the precipitation reactions is the most important parameter. Some properties of the resultant coatings are also presented.

Abstract: We have investigated selective deposition of Co thin films on the OTS-patterned glass surface by using μ-CP(Micro-Contact Printing) coupled with MOCVD(Metal Organic Chemical Vapor Deposition) method with Co2(CO)8 as a Co precursor. Co thin films in the thickness of 5-180 nm has been selectively formed on the glass surface in the presence of the OTS(Octadecyltrichlrosilane) monolayer at the temperatures 60-90
, at the pressure of 0.03-0.6 Torr. The self-assembled OTS monolayer on the surface passivates the surface hydroxyl(-OH), adsorption sites for Co precursors, and thus significantly increases the induction period to nucleate Co metals on the OTS monolayer, compared with on the bare glass. Lowering the temperature and the processing pressure is likely to increase the difference in the induction period for the two substrate surfaces and thus improves the selectivity. About 180 nm-thick Co thin film was selectively formed on the OTS-patterned glass at 70
, however, lowering the temperature to 60
decreased the thickness, which is attributed to the reduced growth rate of Co at the lower temperature. The Co thin films deposited at 60-90
and at 0.03-0.6 Torr have the resistivities of 10-20 μ4-cm and are free of contamination. Consequently, the low temperature process for the selective deposition of Co in the presence of the OTS monolayer can be utilized for a variety of applications including flexible electronics and semiconductor devices.

Abstract: The production of high purity hydrogen gas is an important technical issue for future energy and environmental problem. The pure hydrogen is the ideal fuel in terms of fuel-cell performance. There have been many investigations on the hydrogen permeation of Pd-coated membrane of amorphous alloys. The purpose of this research is to characterize the surface such as roughness and morphology of surface layer of Ni-based amorphous alloy membrane by atomic force microscopy (AFM). The ribbon of Ni-Nb-Ta amorphous alloy was produced by a single-roller melt-spinning technique. The surface characteristic of the amorphous alloy membrane was discussed in view of the hydrogen permeation behavior. From the 3-dimensional AFM images, a lot of hole was observed on the surface of the amorphous alloy membrane produced in air atmosphere. But, a lot of protrusion were observed in the membrane produced in vacuum due to the selective growth on the high oxygen-affinity element of the amorphous alloy. The average roughness of the membrane produced in air atmosphere and vacuum was measured to be 0.359 and 0.263nm, respectively. Therefore, it was considered that it would be suitable to produce the amorphous alloy membrane in vacuum.

Abstract: We discuss the growth kinetics of InAs/GaAs self-assembled quantum dots (QDs) using two different InAs deposition rates, relatively fast growth rate of 0.22 ML/sec and slow growth rate of 0.054 ML/sec. With increasing InAs deposition amount to 3.0 ML, the QD density was almost constant after 2D to 3D island transition at the slow deposition rate while the QD density kept increasing and the QD size distribution was relatively broad at the fast growth rate. After the 2D to 3D transition, at the slow growth rate, further deposited In adatoms seemed to incorporate primarily into already formed islands, and thus contribute to equalize island size. The photoluminescence (PL) full-width at half maximum (FWHM) of 2.5 ML InAs QDs at 0.054 ML/sec was 23 meV at 78K. The PL characteristics of InAs/GaAs QDs were degraded significantly after thermal annealing at 550 oC for 3 hours.

Abstract: The growing importance of high integration on electronics demands novel interconnection methods replacing high-cost solder bumping or less reliable conductive adhesives. Self-organizing interconnection process using resin containing solder fillers has a possibility to achieve high-density joints satisfying both needs. Numerical study visualized the process and revealed that surface tension of molten fillers and resin viscosity determine the speed of conductive path formation.

Abstract: We present the linear stability analysis for the epitaxial thin film growth on the vicinal surface of strained Si and the growth mode diagrams of the epitaxial growth under various operation conditions. Competition between step-step elastic interactions and the asymmetry of incorporation of adatoms from the terraces to step edge is considered. Force monopoles at steps and their interaction lead to it on the vicinal surface while kinetic asymmetry of the adatom incorporation at steps due to Ehrlich-Schwoebel barrier prevents the step bunching instability. Growth mode on the vicinal surface is determined by the competition between elastic step-step interactions and Ehrlich-Schwoebel barrier.

Abstract: We study Si adatom diffusion process near Si/Ge stepped surfaces from first-principles. Dependence of surface growth morphology on growing conditions such as temperature is not clearly understood. We calculate Ehrlich-Schwoebel(ES) barrier of stepped surfaces from first-principles and analyze adatom diffusion process to understand growth mechanism of the surfaces. The configuration of the surfaces with ES barrier would play a key role in the diffusion process because it controls hopping rates in the presence of step edges. Our results are likely to help correctly access the adatom diffusion process on the surfaces.

Abstract: 3D type flower-like ZnO nanostructure is fabricated on GaN epitaxial layer by hydrothermal synthesis. The formation of ZnO nanostructures is controlled dominantly by pH of the aqueous solution. The microstructure of flower-like ZnO nanostructure was examined by FE-SEM, XRD and FE-TEM. It is found that the shape of ZnO nanostructures are likely flower and chestnut bur shapes. FE-TEM and XRD analysis shows that ZnO nanostructures are single crystalline. Some discussion is made on the mechanism of ZnO growth in solutions with different pH.